He hated foster homes.

You think your family can be tough sometimes? Callen spent time in 37 foster homes.

He keeps his apartment sparse.

We've gotten a few glimpses of Callen's home over the years, but on "Cancel Christmas" (Season 7, Episode 11) it was confirmed that he still hasn't done much to dress up the place. Sam even commented on the lack of festive decorations.

He speaks a ton of languages.

Callen has been known to speak Polish, Russian, German, Italian, French, Arabic, Romanian, and Czech. Also, according to Hetty, his Chechen is "passable."

Hetty stepped in the save Callen when he was a teen.

Hetty knew much more about Callen's past than he did when the two met oh-so-long ago. Callen had just spent three weeks in juvenile detention before escaping, robbing a storage locker, stealing a car, and then crashing it. That's when Hetty decided to get involved.

He's been shot. Like, a lot.

Callen has five bullet scars on his back.

His mom served her new country.

Callen’s mother, Clara, was born in Romania, but fled for the United States as a refugee before becoming a CIA agent. Clara eventually returned to Romania, while working for the CIA, and posed as a student (Hetty acted as her CIA handler). She spent six years abroad before she was murdered at the hands of the Comescu family.

He was given a toy soldier before his mother was killed.

For some reason, the people who were behind the killing of Callen's mother gave him a toy soldier to distract him while the assassin completed the job.

He was in the CIA.

Like his mom, Callen worked for The Company.

His relatives were part of a bloody feud.

The Comescus are a Romanian crime family that had an ongoing feud with the Callens since World War II. That's when Callen's grandfather hunted them down for war crimes.

His sister met a terrible fate.

Callen's sister, Amy, was supposedly killed when she fell into the L.A. River.

Callen has magical tendencies.

On a happier note, Callen is no stranger to magic. In Season 1, he went undercover as an illusionist and even owned a rabbit—which he claimed came with the hat that he bought.

He has a strong relationship with Gibbs.

Callen and Gibbs served together at least twice, and Callen is one of the few people Gibbs permits to call him "Jethro."

He's been married. Kinda.

While working undercover, Callen was once married to a CIA double agent named Tracy Rosetti.

He looks good in a tux.

Callen tried to wear his undercover tuxedo out for drinks, but Hetty quickly put a stop to it.

He's spent many years trying to find out who his father is.

Callen's mysterious past includes a mysterious father, who Callen discovered was a possible KGB Major. Though his dad was sent to a labor camp in Siberia, there was no record of his death.

Callen's father assumed the name Konstantin Chernoff.

Hetty came to Callen with information she found in the Kremlin's system after Callen had asked Eric to dig into it for him.

There was man whom Arkady dealt with in Russia until 1988 named Konstantin Chernoff. There are no records of that man before 1974, the year Nikita Reznikov was sent to the Gulag. Hetty and Callen deduced that Callen’s father escaped, then dropped the name Reznikov and assumed the name Chernoff. Chernoff lived in Ruza, about an hour west of Moscow.

There's a tombstone with the name Konstantin Chernoff in Ruza.

Hetty told Callen that Konstantin Chernoff died in 2008 and is buried in the town cemetery in Ruza.

Uncirculated coins like this one had a very special use to Callen's father.

Callen found a rare coin with Lenin's face on it among Arkady's belongings that matched coins Callen has in a box of artifacts about his past.

Hetty identified the coin as very rare because it was minted but never circulated. She mused that—allegedly—Lenin was critical of Russia in his private life. She also told Callen that apparently the coin meant something to his father. Arkady later revealed that he and Callen's father used the coins to communicate about whom they could trust.

Arkady Kolcheck knows more about Callen's past than he's saying.

Arkady Kolcheck may be Callen's only chance of finding out who his father was and where he came from, according to Hetty.

Callen's father was a loyal espresso drinker.

While in Russia, Callen learned that his father was a loyal customer of a cafe there, which had been serving the same espresso from the same machine dating back 100 years.

The Russian cafe might have a photo of Callen's father on the wall.

Arkady told Callen that this photo was taken eight years after his father was supposedly taken to the Gulag—but is that Callen's father in the photo?

If Callen's father is buried in Ruza, who is this guy?

At the end of the Season 6 finale, we saw a man sitting in the cafe that the NCIS team was just in. The man was spinning a coin like the one that Callen and Arkady had while sipping a cup of espresso. Could this man be Callen's father?

Callen's father helped a man named Hans Schreiber.

One of the refugees Callen's father helped escape Russia was Hans Schreiber, a man who kept an eye on Callen for years in return for his freedom. Schreiber was killed by Vasile Comescu before Callen could get any more information from him.

The G stands for Grisha.

When Callen was in Russia to break Arkady out of prison on "Matryoshka, Part 2" (Season 7, Episode 16), he met a local man named Garrison—who we recognize as the man from the cafe in Season 6. During their encounter, Garrison says that Callen's mother wanted him to know where he comes from. We knew that the name "Callen" is from his mother's side of the family, but the G has long been a mystery. Garrison revealed that it's short for Grisha, which comes from his longer name: Grisha Aleksandrovich Nikolaev.

"Do you know who I am?"

Garrison and Callen shared a poignant moment, with Callen indicating that he knew who the man was—and that he wanted to know more. Garrison promised to tell Callen everything at a later time, but they had to split up as the NCIS team fled the country.

His family is bigger than he realized.

Callen's family history is an ever changing, ever evolving tapestry, and in "Glasnost" (Episode 9, Season 8) the special agent learned from his father, Garrison, that he has a half-sister named Alex (played by India de Beaufort) and a young nephew.